Radio terminal device antenna and radio terminal device

ABSTRACT

A radio terminal device has an antenna element, a coil, a switch, an RF circuit section and a conductive substrate. The switch is used to switch between a case where current distribution exists only in the antenna element and its vicinities and a case where the current distribution exists not only in the antenna element and its vicinities but also in other places. Additionally, the switch is switched in accordance with the usage pattern in which the user uses the radio terminal device (e.g., telephone call and data communication). This allows the transmission/reception to be performed with the antenna polarization and directivity suitable for the usage pattern. Thus, there can be provided a radio terminal device that exhibits a reception characteristic suitable for a respective situation.

This application is a U.S. National phase application of PCTInternational Application PCT/2003/12223.

FIELD OF THE INVENTION

The present invention relates to an antenna for a radio terminal deviceand a radio terminal device.

BACKGROUND OF THE INVENTION

In case of the PDC system, as for a conventional antenna for a radioterminal device, a diversity antenna in combination of a whip antenna102 and a planar inverted F antenna 103, as shown in FIG. 20, has beenused well for dealing with a fading problem. However, all of theseantennas have the polarization in which the z-axis directional componentis big. Therefore, in a radio communications systemtransmission/reception in the vertical polarization at the base station,when a portable phone is used for telephone call and data communicationsas shown in FIG. 21, the polarization loss becomes small at the time ofdata communications as the polarization is the same verticalpolarization, while the polarization loss becomes great depending on theslope of a plane of polarization at the time of telephone conversation.

Accordingly, in any states such as telephone call or datacommunications, there was described an antenna from which goodpolarization characteristics can be obtained, for example, inJP-A-2001-326514. FIG. 22 illustrates a conventional radio terminaldevice as described in the aforementioned patent publication.

In FIG. 22, a radio terminal device has one or a plurality of conversionswitches 2202 for switching electrical connection state on an antennaelement 2201 in which the electrical length is approximately 1wavelength for a frequency in use. By switching the conversion switches2202, the main polarization characteristic of an antenna can be switchedto the horizontal polarization and vertical polarization. Meanwhile, aconversion control circuit section 2203 is provided with adiscriminating means of a communication media such as voicecommunications/data communications or a discriminating means to decidewhether any external device is connected to the radio terminal device.By switching the conversion switch 2202 based on the discriminationresults from such discriminating means, the user is able to have a goodplane of polarization automatically without awareness.

Meanwhile, there was mentioned a technique to switch the polarizationand the directivity of an antenna by switching an antenna to thebalanced characteristic and unbalanced characteristic inJP-A-2002-43826. FIG. 23 illustrates a conventional radio terminaldevice as described in the aforementioned patent publication.

In FIG. 23, the radio terminal device is provided with a rectangularloop antenna element 2303 of 1 wavelength arranged in the proximity of aradio substrate 2301 and both ends of the loop antenna element 2303 arebent so as to face toward a feeding section, thus configuring thecurrent distribution that a current in the most front end portionbecomes zero. Also, by concentrating the current on the loop antennaelement 2303, the current component flowing on the radio substrate 2301is reduced and the influence when a human being holds the radio terminaldevice in the hand is suppressed, and the directive characteristic isformed according to the arrival wave at the same time. Furthermore, byadjusting a phase circuit 2304, it is possible to switch the balancedcharacteristic and the unbalanced characteristic or to have a statetherebetween and to form a plurality of radiation directional patternsin one antenna system depending on the environment of use or an arrivalradio wave.

Meanwhile, other than the above JP-A-2002-43826, there was mentionedabout controlling the directivity of an antenna by changing the currentdistribution in JP-A-2001-223514. FIG. 24A and FIG. 24B show aconfiguration of a case current distribution control section of theconventional radio terminal device as described in this patentpublication.

In FIG. 24A, in the case current distribution control section, metalplates 2401 such as an case in a plurality of shapes of strips having apredetermined width are arranged at predetermined intervals, andconnected by means of devices such as a plurality of diodes 2402 or thelike therebetween. Then, by turning ON/OFF the switch 2404 of a biascontrol circuit 2403, voltages applied to diodes 2402 are controlled andthe current distribution is switched.

However, in the conventional method as described in JP-A-2001-326514,there were problems in that an antenna element of approximately 1wavelength was needed, which could not be installed at the case in viewof a configuration of an antenna so that it was difficult to produce asmall-sized terminal. Meanwhile, the conversion switch 2202 served as ameans to switch an impedance matching circuit and switching at the samefrequency band was not considered.

Meanwhile, according to the conventional method as described inJP-A-2002-43826, a small-sized antenna could be produced by using afolded loop antenna, but there was a problem in that the balancedcharacteristic and unbalanced characteristic could not be switched atthe same frequency band as they were switched at the phase circuit.

Also, as for the conventional method as described in JP-A-2001-223514,there was a problem in that many devices such as diodes and the likewere needed for the control of the current distribution.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an antenna for a radioterminal device and a radio terminal device in which a small-sizedproduct can be realized by configuring with an antenna element that isshorter than 1 wavelength and can be installed at an case, and in whichthe antenna characteristic can be switched at the same frequency bandwith a simple component configuration at the same time.

An antenna for a radio terminal device of the present inventioncomprises an antenna element; and an antenna characteristic switchingsection for switching between the states in which a current distributionexists only on and in the vicinity of the antenna element and in which acurrent distribution exists not only on and in the vicinity of theantenna element but also on the other portions.

Meanwhile, an antenna for a radio terminal device of the presentinvention comprises an antenna element; a conductive substrate arrangedclose in parallel to the long side of the antenna element with asufficiently small spacing as compared with the wavelength in a twistedposition relationship; and an antenna characteristic switching section,being connected to one end of the antenna element in the vicinity of theconductive substrate, for changing the state of continuity with theconductive substrate.

According to the above configuration, the polarization and thedirectivity of an antenna can be switched.

Meanwhile, in an antenna for a radio terminal device of the presentinvention, the antenna characteristic switching section has a switch anda coil connected each other in series and one end of the coil isconnected to the antenna element.

Meanwhile, in an antenna for a radio terminal device of the presentinvention, the antenna characteristic switching section has a diode anda coil connected each other in series.

According to the above configuration, the polarization and thedirectivity of an antenna can be switched with a simple configuration sothat a small-sized antenna can be produced.

Meanwhile, in an antenna for a radio terminal device of the presentinvention, any one of a loop antenna, dipole antenna, and diversityantenna is used as the antenna element.

Furthermore, in an antenna for a radio terminal device of the presentinvention, the antenna element is a dipole antenna and also an arrayantenna configured by two antenna elements.

According to the above configuration, a small-sized antenna can beproduced and can be arranged on the case.

Meanwhile, a radio terminal device comprises an antenna element; aconductive substrate arranged close in parallel to the long side of theantenna element with a sufficiently small spacing as compared with thewavelength in a twisted position relationship; an antenna characteristicswitching section, being connected to one end of the antenna element inthe vicinity of the conductive substrate, for changing the state ofcontinuity with the conductive substrate; and an RF circuit sectionconnected to the other end of the antenna element.

Furthermore, a radio terminal device comprises an antenna element; aconductive substrate arranged close in parallel to the long side of theantenna element with a sufficiently small spacing as compared with thewavelength in a twisted position relationship; a RF circuit sectionconnected to one end of the antenna element; and an antennacharacteristic switching section which is connected to the portion inthe vicinity of the end connected with the RF circuit section and inproximity to the conductive substrate, for changing the state ofcontinuity with the conductive substrate, wherein the other end of theantenna element in proximity to the conductive substrate is connected tothe conductive substrate.

Meanwhile, a radio terminal device comprises an antenna element; aconductive substrate arranged close in parallel to the long side of theantenna element with a sufficiently small spacing as compared with thewavelength in a twisted position relationship; a balanced/unbalancedconverter connected to both ends of the antenna element; a RF circuitsection connected to the balanced/unbalanced converter; and an antennacharacteristic switching section being connected to the antenna elementin the vicinity of the conductive substrate, for changing the state ofcontinuity with the conductive substrate.

According to the above configuration, the polarization and thedirectivity of an antenna can be switched with a simple configuration sothat receiving sensitivity can be improved.

Meanwhile, a radio terminal device of the present invention furthercomprises an operating pattern estimator for discriminating whether thepresent communication is a telephone call or a data communication, tonotify the antenna characteristic switching section, wherein the antennacharacteristic switching section performs a predetermined switching onthe basis of the notification. According to this configuration, thepolarization and the directivity of an antenna can be automaticallyswitched according to the usage pattern of the radio terminal device sothat the user can be served with communications without awareness and ina state with much higher sensitivity.

Meanwhile, a radio terminal device of the present invention furthercomprises a propagation environment estimator for detecting at least anyone of a received power, and a polarization or directivity of an arrivalradio wave, to notify the antenna characteristic switching section,wherein the antenna characteristic switching section performs apredetermined switching on the basis of the notification. According tothis configuration, the polarization and the directivity of an antennacan be automatically switched according to the propagation environmentso that the user can be served with communications without awareness andin a state with much higher sensitivity.

Also, a radio terminal device of the present invention further comprisesa tilt detector for detecting the tilt angle of the radio terminaldevice to notify the antenna characteristic switching section, whereinthe antenna characteristic switching section performs a predeterminedswitching on the basis of the notification. According to thisconfiguration, the polarization and the directivity of an antenna can beautomatically switched according to the slope of the radio terminaldevice so that the user can be served with communications withoutawareness and in a state with much higher sensitivity.

Meanwhile, in a radio terminal device of the present invention, theantenna characteristic switching section has a switch and a coil beingconnected each other in series, one end of the coil being connected tothe antenna element.

Furthermore, in a radio terminal device of the present invention, theantenna characteristic switching section has a diode and a coil beingconnected each other in series.

According to the above configuration, the polarization and thedirectivity of an antenna can be switched with a simple configuration sothat a small-sized radio terminal device can be produced.

Meanwhile, in a radio terminal device of the present invention, theantenna element is any one of a loop antenna, dipole antenna, anddiversity antenna.

Furthermore, in a radio terminal device of the present invention, theantenna element is a dipole antenna and also an array antenna configuredby two antenna elements.

According to the above configuration, a small antenna can be arranged ata case so that a small-sized radio terminal device can be produced.

According to the present invention as described above, an antenna inwhich the directivity thereof at the same frequency band is switched canbe realized by a simple configuration. Due to this, a small-sized radioterminal device can be obtained. Meanwhile, by switching the antennacharacteristic according to the usage pattern, the propagationenvironment or the slope of a radio terminal device, the receptioncharacteristic suitable for each situation can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of a radioterminal device in a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a detailed configuration of aradio terminal device in a first embodiment of the present invention.

FIG. 3 is a diagram illustrating a polarization characteristic of aradio terminal device in a first embodiment of the present invention.

FIG. 4A is a block diagram illustrating a detailed configuration of aradio terminal device in a first embodiment of the present invention.

FIG. 4B is a block diagram illustrating a detailed configuration ofanother type of radio terminal device in the first embodiment of thepresent invention.

FIG. 5 is a block diagram illustrating a detailed configuration of athird type of radio terminal device in a first embodiment of the presentinvention.

FIG. 6 is a diagram illustrating a radiation characteristic of anantenna for a radio terminal device in a first embodiment of the presentinvention.

FIG. 7 is a diagram illustrating a radiation characteristic of anantenna for a radio terminal device in a first embodiment of the presentinvention.

FIG. 8 is a diagram illustrating a radiation characteristic of anantenna for a radio terminal device in a first embodiment of the presentinvention.

FIG. 9 is a diagram illustrating a radiation characteristic of anantenna for a radio terminal device in a first embodiment of the presentinvention.

FIG. 10 is a block diagram illustrating a detailed configuration of aradio terminal device in a first embodiment of the present invention.

FIG. 11 is a block diagram illustrating a configuration of a radioterminal device in a third embodiment of the present invention.

FIGS. 12A to 12C are block diagrams illustrating a detailedconfiguration of a radio terminal device in a third embodiment of thepresent invention.

FIG. 13 is a block diagram illustrating a detailed configuration of aradio terminal device in a third embodiment of the present invention.

FIG. 14 is a graph illustrating a receiving power characteristic of anantenna for a radio terminal device in a third embodiment of the presentinvention.

FIG. 15 is a block diagram illustrating a configuration of a radioterminal device in a fourth embodiment of the present invention.

FIG. 16 is a block diagram illustrating a configuration of a radioterminal device in a fifth embodiment of the present invention.

FIG. 17 is a block diagram illustrating a configuration of a radioterminal device in a second embodiment of the present invention.

FIG. 18 is a block diagram illustrating a detailed configuration of aradio terminal device in a fifth embodiment of the present invention.

FIG. 19 is a block diagram illustrating a detailed configuration of aradio terminal device in a sixth embodiment of the present invention.

FIG. 20 is a diagram illustrating a conventional antenna.

FIG. 21 is a diagram illustrating an example of usage patterns of aradio terminal device.

FIG. 22 is a block diagram illustrating a configuration of aconventional radio terminal device.

FIG. 23 is a block diagram illustrating a configuration of aconventional radio terminal device. and

FIGS. 24A and 24B are diagrams illustrating a configuration of a currentdistribution control section of a conventional radio terminal device.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are demonstrated hereinafter withreference to the drawings.

Embodiment 1

FIG. 1 shows a configuration of a radio terminal device of the presentembodiment.

A radio terminal device 301 has an antenna element 302, an antennacharacteristic switching section 303 and a RF circuit section 306. Morespecific configuration example is shown in FIG. 2.

The antenna element 302 is, for example, a turned-up dipole antenna 401of about a half wavelength, placed on a substrate 411 in a symmetricalarrangement. The both ends of the turned-up dipole antenna 401 arebrought close each other, wherein one end is connected to the RF circuitsection 306 and the other end is connected to a conductive substrate 410which is formed on all over the backside of the substrate 411 through athrough-hole. In this configuration, an unbalanced feeding is performed.The conductive substrate 410 in this case corresponds to a conductivesubstrate.

The antenna characteristic switching section 303 has a coil 402 and aswitch 403. The H terminal of the switch 403 is connected to theconductive substrate 410 through a through-hole. This switch 403 changesselectively whether to connect or disconnect to the conductive substrate410.

When the switch 403 is connected to the L terminal side, feeding pointsof the turned-up dipole antenna 401 are connected to the RF circuitsection 306 and the conductive substrate 410. Therefore is provided anunbalanced feeding. However, in the case of a configuration of thepresent embodiment as shown in FIG. 2 wherein the turned-up dipoleantenna 401 is arranged symmetrically with respect to the conductivesubstrate 410, current distribution concentrates on and in the vicinityof the turned-up dipole antenna 401, thereby providing the samecharacteristic as an antenna element in a balanced feeding. Therefore,the polarized wave of the radio terminal device 301 is the one in whichthe component in the y-axis direction is dominant as represented byArrow 501 in FIG. 3.

On the other hand, when the switch 403 is connected to the H terminal,current flows also onto the conductive substrate 410. This phenomenondestroys the balance of the current distribution which concentrates onand in the vicinity of the turned-up dipole antenna 401. Because of thecurrent distribution existing not only on and in the vicinity of theturned-up dipole antenna 401 but also on the conductive substrate 410,there is shown the same characteristic as in the case of an antennaelement which is provided with an unbalanced feeding. Therefore, thepolarized wave of the radio terminal device 301 is the one in which thecomponent in the z-axis direction is dominant as represented by Arrow502 in FIG. 3. That is, by switching the switch 403, the characteristicof an antenna can be switched between a balanced feeding characteristicand an unbalanced feeding characteristic. In this manner, the directionof polarized wave can be changed.

As a switch 403, for example, a SPDT (Single Pole Double Throw) switchcan be used. Any other devices can be substituted if only they have twoor more switching functions. Also, diodes such as a PIN diode can besubstituted for the switch 403, as illustrated in FIG. 4B. Other devicesthan diodes can be substituted if only they have a function to switchover between connection and disconnection to the conductive substrate410. Incidentally, grounding of the switch 403 can be provided at acommon terminal side as shown in FIG. 4A or FIG. 4B.

Furthermore, as shown in FIG. 5, it is also possible to provide a switch403 on the high frequency side where a RF circuit section 306 isarranged. Even in this configuration, the antenna characteristic can beswitched between a balanced feeding characteristic and unbalancedfeeding characteristic. As a result, such an effect is obtainable thatthe direction of a polarized wave can be selectively changed.

FIGS. 6 and 7 show radio directivities of the radio terminal device 301as shown in the block diagram FIG. 2, which are measured in the samefrequency band under the following prerequisite: letting onewavelength=λ, the width W=0.233 λ, the height H=0.067 λ, the gapG=0.0072 λ, and the turned-up dipole antenna 401 has a full lengthL=2W+2H−2G=0.59 λ (namely, length of about 0.5 wavelength). FIG.6 showsa radio directivity where the switch 403 is switched over to the Hterminal to provide an unbalanced feeding characteristic. FIG. 7 shows aradio directivity where the switch 403 is switched over to the Lterminal to provide a balanced feeding characteristic.

Incidentally, FIGS. 8 and 9 show radio directivities of the radioterminal device 301 in the use state of a telephone call mode in which auser holds the radio terminal device 301 in the left hand. FIG. 8 showsa radio directivity where the switch 403 is switched to the H terminalto provide an unbalanced feeding characteristic. FIG. 9 shows a radiodirectivity where the switch 403 is switched to the L terminal toprovide a balanced feeding characteristic.

However, a resonance frequency of the turned-up dipole antenna 401 ischanged in response to the position of a contact point between the coil402 and the turned-up dipole antenna 401 and the value of the coil 402.Therefore it is also possible to adjust the resonance frequency not onlyby the length of antenna elements but also by the contact point and thevalue of the coil.

As described above, in the case that the radio terminal device 301configured in the present embodiment is held in the left hand of a userin a telephone call state, the polarization directivity thereof is likethe followings: when the switch 403 is switched to the H terminal side,the horizontal composition is dominant as shown in FIG. 8; and when theswitch 403 is switched to the L terminal side, the vertical compositionis dominant as shown in FIG. 9.

Herein, in a radio communication system in which transmission/receptionto/from the base station is performed with vertical polarization,polarization loss of the radio terminal device 301 caused is decreasedwhen, in a telephone call mode as shown in FIG. 21 for example, thepolarization shows such a characteristic where a component in the y-axisdirection is dominant as represented by Arrow 501 in FIG. 3 because ofless mismatching in polarization. Meanwhile, in a data communicationmode as shown in FIG. 21, the polarization loss is decreased when thepolarization shows such a characteristic where a component in the z-axisdirection is dominant as represented by Arrow 502 in FIG. 3.

Consequently, when the switch 403 in FIG. 2 is switched to the Lterminal side, the characteristic in-a telephone call mode is good. Andwhen, the switch 403 is switched to the H terminal side, thecharacteristic in a data communication mode is good.

As described above, according to the present embodiment, directivitiesof antenna can be changed in the same frequency band by switchingbetween concentrating the current distribution on and in the vicinity ofthe antenna element and expanding the current distribution not only onand in the vicinity of the antenna element but also onto the conductivesubstrate with the use of the switch 403. In doing so, it is possible toenhance the received power characteristic of the radio terminal device301, in each usage pattern of a telephone call mode and a datacommunication mode.

Incidentally, the antenna element 302 is not limited to a turned-updipole antenna. A folded loop antenna and so forth may be substituted.Also, the same effect is obtainable in a configuration in which anantenna is provided with a balanced feeding through abalanced/unbalanced converter 404 as shown in FIG. 10.

Embodiment 2

FIG. 17 shows a configuration of the radio terminal device of thepresent embodiment. This embodiment has a configuration where anoperating pattern estimator 304 is further added to the radio terminaldevice of Embodiment 1. Any other configuration thereof is the same withEmbodiment 1.

This operating pattern estimator 304, in accordance with the usagepattern of the radio terminal device, is to determine the characteristicof the antenna element 302 suitable for the usage pattern thereof,outputting signals to an antenna characteristic switching section 303for switching the antenna characteristic.

For example, the operating pattern estimator 304 estimates whether theusage pattern of the radio terminal device is a telephone call mode ordata communication mode. This usage pattern estimation is availablebefore communication starts by, for example, detecting whether or notit's a data communication mode (packet communication mode), whether ornot there is a voice input/output through the microphone/speaker, or bydetecting the pre-added signals for discriminating communication modes.The operating pattern estimator 304 issues instructions on the basis ofthese detection results so that the switch 403 can be switched to the Lterminal side in a telephone call mode, and to the H terminal side in adata communication mode.

As described above, according to the present embodiment, polarization tobe used in communication can be automatically changed over in accordancewith its usage pattern. This can reduce the polarization loss incommunication while users are not aware of it. As a result,communication with higher sensitivity can be realized.

Embodiment 3

FIG. 11 shows a configuration of the radio terminal device of thepresent embodiment. This embodiment is different from Embodiment 2 inthat a propagation environment estimator 305 is substituted for theoperating pattern estimator 304.

This propagation environment estimator 305, in accordance with thepropagation environment, is to determine the characteristic of theantenna element 302 suitable for the propagation environment, thusoutputting a signal to an antenna characteristic switching section 303for switching the antenna characteristic.

For example, the propagation environment estimator 305 monitors receivedpower, polarization or direction of arrival radio waves and so on.

FIGS. 12A to 12C show configurations where the direction of an arrivalradio wave is monitored. An antenna element 401 can be connected to thepropagation environment estimator 305 through switches 1401 and 1402.Because the antenna element 401 can also be recognized as an arrayantenna configured by two antenna elements, the propagation environmentestimator 305 can estimate the direction of arrival radio waves that aretransmitted from the base station by further including detection of thephase difference between the two antenna elements or amplitudes. As aresult, it is possible to give instructions for changing the switch 403to the characteristic suitable for its arrival direction.

Incidentally, ability for estimating arrival direction is not limited tothis configuration: similar function is available also in aconfiguration where the propagation environment estimator 305 includesan array antenna.

Meanwhile, in FIG. 12B, the propagation environment estimator 305 isconnected to a RF circuit section 306 to estimate the arrival directionon the basis of the output results obtained by this RF circuit section306. In FIG. 12C, there are provided two RF circuits 306 and estimationfor the arrival direction is made on the basis of the output resultsrespectively obtained by these two RF circuit sections 306.

Next, FIG. 13 shows a configuration to monitor received power. In FIG.13, a received power determination section 1501, which corresponds tothe propagation environment estimator, is to detect received power,issuing instructions for changing a switch 403 to the terminal side withhigher received power. Meanwhile, the received power determinationsection 1501 can be placed anywhere as far as it can monitor receivedpower. For example, it can be included in a RF circuit section 306;alternatively, it can be configured to monitor the output from the RFcircuit section 306.

FIG. 14 shows the characteristics of received power in the cases wherethe switch 403 is connected to the H terminal side and to the L terminalside, assuming that the radio terminal device 301 is held in the lefthand in a telephone call mode while moving. As shown in FIG. 14, even inthe telephone-call usage only, there is a difference not only in thevalue but also in the dropping timing of received power between thecases of the H terminal side and the L terminal side, which can beswitched over by the switch 403. That is to say, there is very lowcorrelation provided. Therefore, the present invention is good forconfiguration of a diversity antenna with low correlation. As describedabove, according to the present embodiment, communication with highersensitivity is available by changing over the polarization to be usedfor communication in accordance with the propagation environment.

Embodiment 4

FIG. 15 shows a configuration of the radio terminal device of thepresent embodiment. This embodiment is different from Embodiment 2 inthat a tilt detector 308 is substituted for the operating patternestimator 304 of Embodiment 2.

This tilt detector 308 is to detect the tilt angle of the radio terminaldevice 301, determine the characteristic of an antenna element 302suitable for the tilt angle, then outputting signals to an antennacharacteristic switching section 303 in order to change over theconnection.

As a tilt detector 308, for example, a tilting switch can be used. Whatis representative as a tilting switch is a well-closed containerincluding balls and bars inside. When the container tilts by itself,balls and bars inside also tilt together to make electrical contactsON/OFF.

By using this, polarization can be changed over as follows: when theradio terminal device, turning around the x-axis in FIG. 3, tilts by 45degrees or more, polarization is to be switched to the direction ofArrow 501; when the radio terminal device tilts by less than 45 degrees,polarization is to be switched to the direction of Arrow 502. As aresult of that, in a radio communication system in which radio waves aretransmitted and received with a fixed polarization from the basestation, it allows the radio terminal device to reduce the polarizationloss caused by the polarization mismatch, thus upgrading the receptioncharacteristic.

Furthermore, in a usage pattern where telephone call mode and datacommunication mode are operated simultaneously like a case of videophoneor a telephone call while operating a packet communication in parallel,it allows the radio terminal device to improve its communicationsensitivity by switching the polarization to be used for communicationin response to the tilt angle of the radio communication terminal.

Embodiment 5

FIG. 16 shows a configuration of the radio terminal device of thepresent embodiment. This embodiment is different from Embodiment 1 inthat the radio terminal device has plural antennas. Specificconfiguration thereof is shown in FIG. 18.

In FIG. 18, an antenna element 2001 and a switch 2002 is added to theoriginal configuration of Embodiment 1. An operating pattern estimator304 is connected to switches 403 and 2002, controlling each of them inresponse to the operating pattern.

For example, in a stand-by mode, the antenna element 2001 with anearly-nondirectional characteristic is to be used because it is betterfor the efficiency of transmission/reception to use a nondirectionalantenna when the disposition state of the radio communication terminalis not known. In this case, in a telephone call mode, the switch 403 isto be set to the L terminal side and the switch 2002 is to be set to theH terminal side. In a data communication mode, the switch 403 is to beset to the H terminal side and the switch 2002 is to be set to the Hterminal side. On the other hand, in a stand-by mode, the switch 403 canbe set to either H/L terminal, and the switch 2002 is to be set to the Lterminal side in order to change over to the antenna element 2001. Inthis manner, it is possible to switch antennas in accordance with thethree situations.

As described above, configuration with plural antenna elements will makeit possible to control the antenna characteristic to be more adaptive tothe operating pattern.

Incidentally, it is also possible to use the propagation environmentestimator of Embodiment 3 or the tilt detector of Embodiment 4 insteadof the operating pattern estimator 304 so that the antenna with the mostadaptive reception characteristic can be selected among plural antennas.

Embodiment 6

FIG. 19 shows a configuration of the radio terminal device of thepresent embodiment. In this embodiment, the radio terminal device has aconfiguration comprising plural antennas and plural RF circuit sections.

In FIG. 19, the radio terminal device further includes an antennaelement 2101, coil 2102, switch 2103, RF circuit section 2106, and asplitter 2107 in addition to the original configuration of Embodiment 1.Herein, the splitter 2107 has a function to separate input signals intothe RF circuit sections 306 and 2106 and combine input signals inputtedfrom the RF circuit sections 306 and 2106.

An antenna configured by the antenna element 401, coil 402, switch 403and the RF circuit section 306, and an antenna configured by the antennaelement 2101, coil 2102, switch 2103 and the RF circuit section 2106 arerespectively changed between an unbalanced feeding characteristic and abalanced feeding characteristic by respectively switching the switch 403and switch 2103. Therefore each antenna can have a differentcharacteristic from the other. In this manner, like the case as shown inFIG. 14 of Embodiment 3, it is possible to configure a radio terminaldevice having two antennas, the received power characteristics thereofhaving very low correlation.

The above configuration can also be applied to antennas for MIMO (MultiInput Multi Output) system by setting the switch 403 to the L terminalside so that the antenna element 401 may be provided with the balancedfeeding characteristic and by setting the switch 2103 to the H terminalside so that the antenna element 2101 may be provided with theunbalanced feeding characteristic. Meanwhile, MIMO is exemplified byBLAST (Bell Labs Layered Space-Time).

Also, the present invention can be applied to a multiple polarizationsystem because it can transmit and receive two kinds of polarized wavesas shown in FIG. 3 by switching-over the switches.

Furthermore, this invention can realize transmission diversity and canalso be applied to antennas for receiving or transmitting space and timecodes, adaptive array antennas having two antenna elements and so forth.

Further, in a case of using the radio terminal device held in one hand,influence of the hand will be reduced by providing the antenna elementcloser to the hand with unbalanced feeding characteristic.

Meanwhile, such a configuration is also possible wherein thecharacteristic of one or both of the antennas are fixed without usingswitches.

INDUSTRIAL APPLICABILITY

An antenna for a radio terminal device and a radio terminal deviceaccording to the present invention are useful in the radio terminaldevice necessary for switching the antenna characteristic and suitablefor reduction in the size.

1. An antenna for a radio terminal device comprising: (a) an antennaelement; (b) and an antenna characteristic switching section forswitching the antenna characteristic between a balanced feedingcharacteristics and an unbalanced feeding characteristics by switchingbetween states in which a current distribution exists only on and in avicinity of the antenna element and in which the current distributionexists not only on and in the vicinity of the antenna element but alsoon other portions.
 2. An antenna for a radio terminal device accordingto claim 1, wherein the antenna element is connected with a conductivesubstrate arranged close in parallel to a long side of the antennaelement with a sufficiently small spacing as compared with a wavelengthin a twisted position relationship, and the antenna characteristicswitching section is connected to one end of the antenna element in avicinity of the conductive substrate, for changing a state of continuitywith the conductive substrate.
 3. An antenna for a radio terminal deviceaccording to claim 1, wherein any one of a loop antenna, a dipoleantenna, and a diversity antenna is used as the antenna element.
 4. Anantenna for a radio terminal device comprising: (a) an antenna element;and (b) an antenna characteristic switching section for switchingbetween states in which a current distribution exists only on and in avicinity of the antenna element and in which the current distributionexists not only on and in the vicinity of the antenna element but alsoon other portions, wherein the antenna characteristic switching sectionhas either of a switch and a diode, and a coil connected to each otherin series.
 5. An antenna for a radio terminal device according to claim4, wherein the antenna element is a dipole antenna and also an arrayantenna configured by two antenna elements.
 6. A radio terminal devicecomprising: (a) an antenna for a radio terminal device, said antennaincluding: (1) an antenna element, and (2) an antenna characteristicswitching section for switching the antenna characteristic between abalanced feeding characteristics and an unbalanced feedingcharacteristics by switching between states in which a currentdistribution exists only on and in a vicinity of the antenna element andin which the current distribution exists not only on and in the vicinityof the antenna element but also on other portions; and (b) a RF circuitsection connected to one end of the antenna element.
 7. A radio terminaldevice according to claim 6, wherein the antenna element is any one of aloop antenna, a dipole antenna, and a diversity antenna.
 8. A radioterminal device comprising; (a) an antenna for a radio terminal device,said antenna including: (1) an antenna element, and (2) an antennacharacteristic switching section for switching between states in which acurrent distribution exists only on and in a vicinity of the antennaelement and in which the current distribution exists not only on and inthe vicinity of the antenna element but also on other portions; and (b)a RF circuit section connected to one end of the antenna element,wherein the antenna element is connected with a conductive substratearranged close in parallel to a long side of the antenna element with asufficiently small spacing as compared with a wavelength in a twistedposition relationship, and the antenna characteristic switching sectionis connected to an other end of the antenna element in a vicinity of theconductive substrate, for changing a state of continuity with theconductive substrate.
 9. A radio terminal device according to claim 8,further comprising: an operating pattern estimator for discriminatingwhether a present communication media is a telephone call or a datacommunication, to notify the antenna characteristic switching section,wherein the antenna characteristic switching section performs apredetermined switching on the basis of the notification.
 10. A radioterminal device according to claim 8, further comprising: a propagationenvironment estimator for detecting a received power, a polarization ofan arrival radio wave or a direction of an arrival radio wave, to notifythe antenna characteristic switching section, wherein the antennacharacteristic switching section performs a predetermined switching onthe basis of the notification.
 11. A radio terminal device according toclaim 8, further comprising: a tilt detector for detecting a tilt angleof the radio terminal device to notify the antenna characteristicswitching section, wherein the antenna characteristic switching sectionperforms a predetermined switching on the basis of the notification. 12.A radio terminal device according to claim 8, wherein the antennacharacteristic switching section has either of a switch and a diode, anda coil being connected to each other in series, one end of the coilbeing connected to said antenna element.
 13. A radio terminal deviceaccording to claim 8, wherein the antenna element is a dipole antennaand also an array antenna configured by two antenna elements.
 14. Aradio terminal device according to claim 8, further comprising: afurther antenna element that is used in a stand-by mode.
 15. A radioterminal device according to claim 8, wherein the antenna includes oneor more sets of antennas paired with a respective two or more RF circuitsections, the radio terminal device further comprising: a splitter whichcombines signals from said two or more RE circuit sections, or divides asignal into the respective RF circuit sections, wherein the splitterconnects with the respective RF circuit sections.
 16. A radio terminaldevice comprising: (a) an antenna element; (b) a conductive substratearranged close in parallel to a long side of the antenna element with asufficiently small spacing as compared with a wavelength in a twistedposition relationship; (c) a balanced/unbalanced converter connected toboth ends of the antenna element; (d) a RF circuit section connected tosaid antenna element through said balanced/unbalanced converter; and (e)an antenna characteristic switching section connected to the antennaelement in a vicinity of the conductive substrate, for changing a stateof continuity with the conductive substrate.
 17. A radio terminal deviceaccording to claim 16, further comprising: an operating patternestimator for discriminating whether a present communication media is atelephone call or a data communication, to notify the antennacharacteristic switching section, wherein the antenna characteristicswitching section performs a predetermined switching on the basis of thenotification.
 18. A radio terminal device according to claim 16, furthercomprising: a propagation environment estimator for detecting a receivedpower or a polarization and direction of an arrival radio wave, tonotify the antenna characteristic switching section, wherein the antennacharacteristic switching section performs a predetermined switching onthe basis of the notification.
 19. A radio terminal device according toclaim 16, further comprising: a tilt detector for detecting a tilt angleof the radio terminal device to notify the antenna characteristicswitching section, wherein the antenna characteristic switching sectionperforms a predetermined switching on the basis of the notification. 20.A radio terminal device according to claim 16, wherein the antennacharacteristic switching section has either of a switch and a diode, anda coil being connected to each other in series, one end of the coilbeing connected to said antenna element.
 21. A radio terminal deviceaccording to claim 16, wherein the antenna element is a dipole antennaand also an array antenna configured by two antenna elements.
 22. Aradio terminal device according to claim 16, wherein the antenna elementis connected with the conductive substrates, and the antennacharacteristic switching section is connected to one end of the antennaelement in the vicinity of the conductive substrate.